1. Field of the Invention
The present invention relates to a honeycomb structure.
2. Description of the Related Art
Conventionally, honeycomb structures are employed in exhaust gas treatment apparatuses used for treating NOx and the like in exhaust gases of automobiles (e.g. JP-A-2006-183477).
Such a honeycomb structure has, for example, plural cells (through-holes) extending in the longitudinal direction from one end face of the honeycomb structure to the other end face, and these cells are separated from each other by cell walls.
The cell walls of the honeycomb structure are made of ceramics, such as cordierite, and a NOx adsorbent material and an ammonia adsorbent material are provided on the cell walls. As the NOx adsorbent material, ceria or the like is used. On a layer constituted of the NOx adsorbent material, a noble metal catalyst, such as platinum, is supported. As the ammonia adsorbent material, zeolite or the like is used.
When the exhaust gas of an automobile or the like, for example, passes through such a honeycomb structure, NOx in the exhaust gas is converted according to the following cycle: in the case where the exhaust gas is an oxidizing atmosphere (for example, during normal operation of a diesel engine), NOx in the exhaust gas is adsorbed on the NOx adsorbent material; then, when the exhaust gas is switched to a reducing atmosphere (for example, during rich spike control of the diesel engine), the adsorbed NOx is reduced on the catalyst, resulting in producing ammonia, which is then adsorbed on the ammonia adsorbent material; and when the exhaust gas is switched back to an oxidizing atmosphere, NOx is reduced again with the use of the adsorbed ammonia, and if the adsorbed ammonia is consumed, then NOx is adsorbed on the NOx adsorbent material.
Accordingly, by passing the exhaust gases through a honeycomb structure, NOx in the exhaust gases can be converted. Meanwhile, honeycomb structures comprising inorganic particles, inorganic fibers and inorganic binder have come to be known (e.g. WO2005/063653A1).
The contents of JP-A-2006-183477 and WO2005/063653A1 are incorporated herein by reference.